Asphaltic sheet materials are widely used in the construction industry. For example, polymer-modified asphaltic sheet material is used as membrane for waterproofing flat or low-sloped roofs. As is known in the art, these roofing systems may include multiple layers of asphaltic sheet including base sheets and cap sheets. Other examples include barriers materials such air, vapor, or moisture barriers. These materials are typically used on roofs or vertical surfaces such as walls to provide the desired air, vapor and/or moisture resistance to a structure. Still other examples include underlayments, which are used in the roofing industry to provide an extra layer of protection to the roof. This additional protection may provide, among other benefits, water, moisture, thermal, and/or fire resistance. As the name implies, underlayment is typically positioned below the external or primary roofing protection, which may include shingles, membranes such as polymeric or asphaltic membranes, roofing tiles, and metal panels or cladding.
In order to meet certain fire resistance properties, which may be required by code or classification, fire or flame resistant asphaltic sheet may be employed. As is known in the art, asphaltic sheet can be provided with a degree of fire or flame resistance by including therein fire or flame retardant materials. Many flame retardant materials have been proposed including, for example, intumescent materials as suggested by U.S. Pat. No. 5,516,817. Intumescent materials operate by forming a char layer that is believed to mitigate flame spread over more flammable materials by impeding the oxygen supply to those more flammable materials.
The use of intumescent materials, however, can be problematic because the temperatures at which the asphaltic sheet can be manufactured or processed must be below the temperature at which the char layer forms. Indeed, if the processing temperature of the asphaltic sheet is above the temperature at which the intumescent materials forms a char, then the manufacture of the desired product is frustrated, if not precluded.
Because the use of intumescent materials as flame retardants in asphaltic sheet is believed to be advantageous, there is a need to develop manufacturing techniques that allow for the inclusion of intumescent materials into the asphaltic sheet without triggering the char-forming behavior of the intumescent material. Indeed, in so doing, the scope of useful intumescent materials can be expanded.